Absorbent articles such as disposable diapers are manufactured by performing a process such as embossing and heat-seal processing to a plurality of semi-finished products transported in an aligned manner in a transporting direction in its production line. In order to reject poorly processed semi-finished products, an inspection is performed during the transportation of the semi-finished products.
As an illustrative example of such an inspection method, PTL 1 discloses a method using an infrared camera. That is to say, an image of a temperature distribution in a semi-finished product is acquired by imaging each semi-finished product, which is being transported, with an infrared camera, an actual processing position is specified on the basis of a contour position of the semi-finished product by processing the image by a process such as binarization, and it is determined whether or not the specified processing position is within an allowable range of a regular process target position determined by the contour position.